The disclosure relates to gas turbine engines. More particularly, the disclosure relates to turbofan engines with thrust augmentation.
Conventional gas turbine engines have, in serial axial flow relation from upstream to downstream and fore to aft: at least one compressor section to compress inlet air; a combustor to add fuel to the pressurized air and ignite/combust the mixture; and one or more turbine sections to extract work from and expand the combustion gases.
Each compressor section and turbine section may comprise one or more circumferential stages of blades mounted for rotation about the engine centerline and one or more stages of vanes interspersed with the blades and non-rotating about the centerline. Some vanes may be mounted for controlled rotation about near radial axes to provide controllable pitch or angle of attack. In a basic two-spool engine, the blades of one compressor section are driven by the blades of one turbine section and the blades of the other compressor section are driven by the blades of the other turbine section. In particular, the upstream compressor section is a low pressure compressor (LPC) section which is coupled to the downstream turbine section which is a low pressure turbine (LPT) section. These may be coupled by an associated shaft (“low pressure shaft” or “low spool shaft”). Similarly, the downstream compressor section is a high pressure compressor (HPC) coupled to the upstream turbine section (a high pressure turbine (HPT)) via a shaft. Other two-spool examples have but a single compressor section driven by the HPT and with the LPT driving only the fan.
In exemplary engines, at normal operating conditions, the high pressure shaft rotates faster than the low pressure shaft and therefore that shaft, its spool and compressor and turbine sections are often referred to as “high speed” whereas the low pressure sections are referred to as “low speed”.
Other configurations of engines involve three spools or yet different configurations such as counterrotating blades replacing vanes.
Many engines are turbofan engines wherein a fan section is upstream of the compressor section(s). The fan drives air downstream with some air passing into the compressor and additional air bypassing the compressor. In such turbofan engines, the compressor section(s), combustor, and turbine section(s) are often referred to as the “core” with the core flowpath passing sequentially therethrough. The bypass air bypasses these (at least bypassing the compressor) and passes along a bypass flowpath. There are often diversions/branches directing portions of the bypass air to cool various components and/or provide process dilution.
Many military turbofan engines include afterburners or augmentors. In an exemplary augmentor, additional fuel is introduced (via spraying) downstream of the turbine section(s) into the exhaust (or into a combined flow of the core exhaust with bypass air).
There have been a number of proposals for replacing conventional afterburners and/or augmentors with alternative thrust augmentation systems. Two of several proposals are seen in US Pregrant Publications 2009/0211221 and 2009/0211222.
Separately, a class of engines has been developed called tip turbine engines (TTEs). Examples of these are found in US Pregrant Publications 2003/0192303, 2003/0192304, and 2004/0024590. More recent examples of these are seen in US Pregrant Publication 2008/0124211 and U.S. Pat. Nos. 8,061,968, 7,921,635, 8,033,092, 7,882,694, 7,878,762, 7,607,286, 7,921,636, and 7201558.
An exemplary TTE comprises a centrifugal compressor whose rotor also provides one or more turbine blade stages. In various examples, the centrifugal compressor may be downstream of and coupled to an axial compressor. The centrifugal compressor rotor also forms a fan to drive an airflow (e.g., downstream along an annular flowpath). The combustor may be positioned in a nacelle or other structure outboard of that axial fan path.